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Affiliation
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Department of Orthopaedic and Trauma Surgery, The Great Western Hospital, Marlborough Road, Swindon, Wiltshire SN3 6BB, UK |
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Abstract
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Rupture of the distal tendon of the biceps brachii is a rare injury which has previously been thought to represent 3% of all ruptures of biceps brachii. The incidence of this injury has been estimated at 1.2 per 100,000 population per year. Although rare, the injury does appear to be most commonly caused by an unintentional eccentric load to a flexed elbow with a shortened and contracted muscle forcing the joint into extension. Risk factors for rupture of the distal tendon of biceps are thought to include both local and systemic factors. Local factors, such as increased functional demand (which may occur in heavy manual labour or weight lifting) are implicated and a theory of repetitive minor trauma and hypoxia caused by mechanical impingement of biceps tendon during forearm rotation has been proposed. Systemic factors such as smoking, steroid use, hypercholesterolaemia, obesity and diabetes mellitus are also implicated. As previously reported, in most cases of rupture, tendon degeneration and subsequent rupture has a multi-factorial aetiology with a mixture of predisposing hereditary, structural, overuse and social factors.
Rupture of the distal tendon may lead to a significant functional deficit with both a reduction of power and a decrease in range of movement of flexion at the elbow and supination of the forearm. We report two cases of rupture of the distal biceps tendon which had been sustained in the process of using 'button' lifts on skiing holidays.
Previously described mechanisms of rupture of distal biceps tendon include weight lifting, 'spotting' gymnasts, carrying and catching heavy loads and ten pin bowling.
Although the overall injury rate for skiers is known to be between two and five skier injuries per 1000 skiing days, a thorough literature search has not revealed any previously described cases where rupture of the distal biceps tendon has resulted from the use of the drag lift in ski resorts. Both patients reported the flexed elbow being subject to an eccentric load forcing the arm into extension which supports this as the likely mechanism to cause rupture.
The principle of the drag lift is that once the bar is 'loaded' with the mass of a skier, the coiled drag cable is gradually released with increasing tension until the tensile force in the cable is enough to overcome the force of resistance caused by the mass of the skier, the force of gravity, the co-efficient of friction between skis and snow and the effect of the angle of the slope. When the cable force exceeds this combined force of resistance, motion is initiated and the skier will then be accelerated to the speed of the drag lift. The ski lift operators and designers clearly have to accommodate a wide range of skiers of varying weights. Snow conditions (and therefore co-efficient of friction) will always be changeable throughout a ski season and gravity is clearly a constant. The 'spring boxes' which allow progressive loading of the individual drag cables are manufactured to regulation standards and lift operators cannot change these. This means that ski lift operators can only influence two remaining factors.
One factor is the initial gradient of the drag-lift run up which the skier is being 'dragged' and the other is the speed at which the drag lift runs. The area where a skier 'catches' the drag-lift is known as the loading area and guidelines from ski-lift manufacturers state that this loading area should be without an incline (Harrusch Lift Manufacturers). Both cases reported a slight incline at the loading area involved. The other factor which can be influenced is the speed of the lift. Most drag lifts run at speeds of between 300 and 400 feet per minute which can be changed by lift operators. Faster lift speeds cause a more sudden loading of the drag cable which would increase the risk of tendon rupture or other injury.
If injuries such as the tendon ruptures here described are occurring as a result of drag lift use, we suggest that either the gradient of incline at the loading area of the lift is too steep or that the speed at which the drag cable runs is too great. Both of these factors could easily be addressed and we suggest that the issue (and implementation) of guidelines to ski lift operators regarding optimal gradient of incline and optimal lift speed may help avoid the excessive eccentric load on distal biceps tendon which can lead to rupture. |